Now at the end of a list of your extensions (ctrl shift E), you can tap on Extension Keyboard Shortcuts, and then if you get the DDG extension, you can give it a keyboard shortcut. I made mine Alt-d.

If I hold the alt key down, and press d, a bar for DDG opens with the cursor already in that bar. So I can instantly start typing my DDG search query in that bar.

Alternatively, you can go add DDG as a search engine, by going to the website of DDG, https://duckduckgo.com/ and right click on the DDG search bar. Click on create search engine. Then you get a shortcut, let's say d. So if you're at the main Opera address bar in your browser, just type d [space] before your search query in that main address bar.

You thus have two quick ways of doing your DDG searches, depending on where you cursor is, and which shortcut is easier to get to for you. I use both.